<!DOCTYPE html>
<html lang="en">
<head>
    <meta charset="UTF-8">
    <title>Title</title>
</head>

<body>
  <canvas id="myCanvas" width="200" height="100"></canvas>
  <script type="text/javascript">

      var c=document.getElementById("myCanvas");

      var cxt=c.getContext("2d");

      cxt.fillStyle="#FF0000";

      cxt.fillRect(0,0,150,75);

  </script>
</body>
</html>